THE Sun was such a tempestuous baby that it scattered radioactive atoms all
over our developing Solar System, say astronomers using NASA鈥檚 Chandra X-ray
Observatory. They conclude our Sun was prone to these temper tantrums after
spying a few other stormy youngsters.
If they are right, it may solve a mystery surrounding the birth of the Solar
System. Astrophysicists think that all atoms heavier than helium on Earth and
the other planets were created many billions of years ago by an earlier
generation of large stars. When they exploded they scattered the atoms through
space. But some atoms don鈥檛 fit this theory.
Many meteorites contain atoms formed by the decay of unusual radioactive
atoms, mainly isotopes of aluminium and calcium. These atoms survive just a few
billion years, which means they had to be created around the time the Solar
System was born.
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The trouble is, researchers believe that the birth of the Solar System was a
fairly unexciting event, with a gas cloud quietly collapsing into a medium-sized
young star and a dust disc coalescing into planets. What could have provided the
energy needed to create these unusual isotopes?
One theory is that a huge star exploded nearby just as the Solar System was
created, says Donald Clayton of Clemson University in South Carolina. But
supernovae are very rare events, so this would have been an amazing coincidence.
鈥淚n this view our Solar System is somewhat special,鈥� says Clayton.
But there may be a simpler explanation, says a team from Pennsylvania State
University in University Park, and Massachusetts Institute of Technology. At a
symposium in Washington DC last week to mark Chandra鈥檚 first two years in orbit,
they announced they had captured an image of the Orion nebula containing 31
young stars about the same size as our Sun. To their surprise, all of these
stars are highly energetic. 鈥淭hey鈥檙e emitting X-ray flares 100 times more
powerful and 100 times as often as our Sun does today,鈥� says team member Eric
Feigelson.
These young stars must be emitting huge numbers of protons with more than
enough energy to trigger fission in heavy elements in a dust disc. This might
explain how the isotopes found in meteorites were formed in the early Solar
System.